Central Venous Pressure (CVP) — Anaesthesia Notes

1. Definition

CVP = pressure in the superior vena cava / right atrium ≈ right atrial pressure (RAP)

Reflects:

RV preload
Circulating blood volume
Venous tone
RV performance

Normal CVP: 2–8 mmHg

2. Physiological Basis

Factor	Effect on CVP
Hypovolaemia	↓
Right heart failure	↑
Cardiac tamponade	↑
Tension pneumothorax	↑
PEEP	↑
Vasodilation (sepsis, anaesthesia)	↓
Tricuspid regurgitation	↑ (ventricularised)

CVP reflects right-sided heart function — NOT left ventricular performance. (Barash Clinical Anaesthesia 9e)

3. Indications for CVC Insertion

CVP monitoring in haemodynamically unstable patients and major surgery
Transvenous cardiac pacing
Infusion of vasoactive drugs, TPN, chemotherapy, vesicant agents
Rapid fluid resuscitation (large-bore introducer)
Pulmonary artery catheterisation
Aspiration of air emboli
No peripheral access; repeated blood sampling

4. Access Sites

Site	Key Points
Right IJ	Highest success; direct route to RA/RV; preferred for pacing + PA catheter
Subclavian	Highest pneumothorax risk — avoid in emphysema and OLV cases
Left IJ / EJ	3–5 cm longer to SVC; EJ kinks in lateral decubitus (problem in thoracotomy)
Femoral	Useful when neck immobilised (trauma); infection risk

Site selection:

Coagulopathy → IJ or EJ (compressible); avoid subclavian
Emergency pacing → right IJ (most direct to RV)
Trauma with cervical collar → femoral or subclavian
OLV / thoracic surgery → avoid subclavian; avoid EJ (Barash 9e)

5. CVP Waveform — Normal Components

(Miller's Anaesthesia 10e — Table 32.3)

Wave	Phase	Mechanical Event	ECG timing
a	End-diastole	Atrial contraction (atrial kick)	After P wave
c	Early systole	Tricuspid closure + isovolumic RV contraction	End QRS
x descent	Mid-systole	Atrial relaxation + annular descent	Before T wave
v	Late systole	Venous atrial filling (tricuspid still closed)	After T wave
y descent	Early diastole	Tricuspid opens; RA → RV filling	Before next P
h wave	Mid-diastole	Plateau (only at slow HR or high CVP)	—

Mnemonic: atrial contraction → closure of tricuspid → exit (atrial relaxation) → venous filling → yield to ventricle

CVP waveform correlated with ECG — a, c, x, v, y components. (Fishman's Pulmonary Diseases 5e)

Read CVP at the base of the c wave at end-expiration

6. CVP Waveform Abnormalities

Condition	Change	Mechanism
Atrial fibrillation	Loss of a wave	No organised atrial contraction
AV dissociation	Cannon a waves	Atrium contracts against closed tricuspid
Tricuspid regurgitation	Tall systolic c-v wave; loss of x descent	Regurgitant RA filling in systole
Tricuspid stenosis	Tall a wave; attenuated y descent	Impaired diastolic RA emptying
Cardiac tamponade	Dominant x descent; absent/attenuated y	Extrinsic compression; impaired diastolic filling
Pericardial constriction	Steep x AND y descents; M/W pattern	Exaggerated pressure equalisation
RV ischaemia / infarction	Tall a + v; steep x + y; M/W pattern	Reduced RV compliance

7. Measurement — Practical Points

Zero reference: 5 cm below sternal angle OR mid-thoracic level (phlebostatic axis)
Always consistent levelling throughout monitoring period
Measure at end-expiration (both spontaneous and PPV)
PEEP artificially elevates CVP — factor this in
Use ultrasound guidance (strongly recommended; mandatory for IJ per most guidelines) (Miller's 10e)

8. CVP and Fluid Responsiveness

CVP is a POOR predictor of fluid responsiveness. Multiple RCTs and systematic reviews confirm:

No reliable relationship between CVP and circulating blood volume
A single static CVP cannot predict haemodynamic response to a fluid bolus
Guidelines recommend dynamic variables instead:

Dynamic Variable	Method
Pulse pressure variation (PPV)	Arterial line
Stroke volume variation (SVV)	LiDCO / Vigileo
Passive leg raise (PLR)	Clinical
Oesophageal Doppler	Probe
Point-of-care echocardiography (POCUS)	TOE / TTE

(Fishman's Pulmonary 5e; Miller's Anaesthesia 10e)

9. CVP in Shock

Shock Type	Expected CVP
Hypovolaemic	↓ Low
Distributive (sepsis, anaphylaxis)	↓ Low
Cardiogenic (right heart failure)	↑ High
Obstructive (tamponade, tension PTX, massive PE)	↑ High

10. Complications

Up to 15% of patients experience some adverse event. (Miller's 10e)

Mechanical

Arterial puncture (1.9–15%) — most common acute complication
Pneumothorax (↑ subclavian)
Haemothorax / hydrothorax / chylothorax (L subclavian)
Air embolism
Catheter malposition, arrhythmias (guide wire in RV)

Thromboembolic

DVT, PE, catheter-related thrombosis

Infectious

CLABSI (central line-associated bloodstream infection)
Prevention: chlorhexidine prep, maximal sterile barrier, insertion checklist, daily need review

11. Exam Summary — 10 High-Yield Facts

CVP = RAP ≈ RV preload — not LV preload
Normal: 2–8 mmHg; read at end-expiration, base of c wave
Waveform: a, c, v peaks; x, y descents — timed against ECG
Cannon a waves = AV dissociation; loss of a = AF; c-v fusion + no x = tricuspid regurgitation
Tamponade: dominant x descent, absent y — Constriction: steep x AND y (M/W)
CVP is a poor predictor of fluid responsiveness — dynamic variables preferred
Right IJ = best site for pacing wires and PA catheters
Subclavian = highest pneumothorax risk; avoid in emphysema and OLV
EJ kinks in lateral decubitus — avoid for thoracotomy
Always use ultrasound guidance; complications occur in up to 15% of insertions

Sources: Miller's Anaesthesia 10e; Barash, Cullen & Stoelting's Clinical Anaesthesia 9e; Fishman's Pulmonary Diseases and Disorders 5e; Morgan & Mikhail's Clinical Anaesthesiology 7e

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